Using wind-induced depressurizations to help houses withstand hurricanes

ABSTRACT

An affordable “non-surgical” method for retro-upgrading a house to better withstand hurricane winds and rain is described, wherein the winds&#39; most strongly depressurized eddies or “Separation Zones” bordering the building envelope are clearly identified and “harnessed” by assured venting of the interior space just into such, thereby depressurizing the interior likewise and strongly reducing or eliminating any net outward-acting force on the building envelope. The “harnessing” is assured simply by installing one-way valves over the vent openings, whereby air can pass outward from the interior to strongest-depressurized Separation Zones but inward flows (such as on the windward) are quickly blocked by the other valved vents “blowing closed”. The roof envelope surrounding the attic is especially addressed, wherein winds from any direction will strongly depressurize the attic and so help hold the roof sheathing down, gables on, soffits and ceiling up—while the valves also block ruinous rain entry on the windward.

BACKGROUND OF THE INVENTION

Hurricane-force winds commonly cause serious damage to a house or similarly framed small building as parts of the roof envelope (sheathing, gables, soffits) are forced off the roof framing, or the whole roof structure is torn off the supporting sidewalls, and/or sidewalls and windows are blown out.

During construction, all connections are accessible and can be readily and effectively done, and improved practice is now generally followed in high-risk areas of the US. In most existing houses at risk, however—over 30 million in the US hurricane belt and tornado-prone regions—both the envelope fastening and structural connections are generally inadequate in the face of increasingly common Category 4 and 5 winds, and the connections are not easily accessed for reinforcing.

Accordingly, a method has been developed to let the winds induce indoor depressurization to counteract the wind-induced external depressurizations, reducing net outward-acting pressure differentials and so helping especially the roof envelope and structure to stay in place (U.S. Pat. No. 6,484,459, entitled COUNTER-PRESSURE METHOD AND APPARATUS FOR PROTECTING ROOFS AGAINST HURRICANES, issued to Robert E. Platts on Nov. 26, 2002.) This method involves equipping existing windows with one-way valves (valved shutters, normally, with windows opened); the valves remain closed or blow closed on the windward but open freely on the leeward, so that the indoor air communicates only with the low-pressure lee-side air and so is itself depressurized. (The depressurization can be extended to include attic air too, it is shown therein, by opening an attic hatch and either closing off all roof vents or valving them as well.)

There are significant limitations and drawbacks entailed with that “counter-pressure” method, however. The leeside depressurization is not very strong, so that harnessing it to depressurize the indoors can counteract just a fraction of the worst depressurizations over-roof and elsewhere around the house. And of course “shuttering up” itself calls for the householder's or others' attention and time. Further, and perhaps most significantly, the indoor depressurization increases the net inward pressure on the building envelope not only where desired but also where some common components are already prone to failing inwardly—notably fixed windward windows, shuttered or not; full-height gable walls where there's no mid-height support from a ceiling; and ceilings themselves, downward of course—inviting ruinous breaches.

Therefore there is a need for providing a much more effective “counter-pressure” method for protecting existing houses, an “always ready” method that assures strongest hold-together depressurizations just where needed while avoiding inward overloading of windows or any other inwardly-weak parts of the building envelope. The present invention arose from a much closer examination of both the house structure and wind action around it, and particularly addresses the crucially important roof envelope enclosing the attic.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a method for upgrading building envelopes against windstorms “non-surgically”, without having to access existing connections to reinforce them.

It is another object of the present invention to provide a method to maintain an interior space at strongly reduced pressures during windstorms to reduce net outward-acting pressures on its envelope, to help keep the envelope intact.

It is a particular object of this invention to provide a method to maintain a house attic at strongly reduced pressures during windstorms to reduce or eliminate net outward-acting pressures on its envelope, including net downward-acting pressure on the ceiling, to help keep all intact.

It is a still further object of the present invention to bar the entry of rain into the attic.

Terms: For greater certainty some terms used herein are defined as follows: “Envelope” refers to a complete or partial area of a building exterior that separates the outdoors from the whole of the building's interior or from an interior space that is itself closed off from other interior spaces. “Roof envelope” refers to the whole of the envelope enclosing the attic (or “roof space”): roof sheathing, gables, soffits and such separating attic from outdoors, and also the ceiling separating it from the indoor space below. “Soffits” are the closures under the roof overhangs bordering the building's exterior walls. (The space enclosed by the overhanging roof and the soffit thereunder, often referred to as the “soffit space”, is almost invariably well connected with the roof space or attic and is here considered as attic.) “Roof structure” refers to that envelope plus of course the roof framing (rafters, trusses) that are connected to the underlying house, generally by way of the exterior walls, and may include the ceiling too. “Separation Zone” (“SZ” for short) is a technical term here used for the depressurized “eddy” location where a wind's momentum as it blows past a corner of a building tends to carry it away from the immediately downstream wall or roof surface, leaving a partial vacuum against such surface beyond that corner. (“Depressurized” and “negative pressure” here signify pressure reductions below ambient atmospheric pressures; “pressurized” and “positive”, the opposite.) “Corner” generally refers to plan view corners where sidewalls meet but also to elevational view corners: where a roof ridge or the junction of an exterior wall with a roof forms a sharp corner, as main examples. “Wind direction” refers to the direction from which it comes. “Inward” infers toward the interior of a building; “outward”, the opposite.

In general terms there is a counter-pressure method for reducing a windstorm's outward-acting forces on a building envelope which comprises: identifying the locations immediately bounding the building's perimeter walls where the most strongly depressurized Separation Zones will be created by winds flowing around and over the building envelope from directions to which the building lies exposed; providing openings or utilizing existing openings through the building envelope facing into such potentially most depressurized Separation Zones to ensure that at least one such opening faces into at least one such Separation Zone created by any wind to which the building lies exposed; fitting a one-way valve over or within each such opening which freely allows outward air flow from the building's interior while remaining closed or closing to bar appreciable inward flow; closing or similarly valving other openings in the envelope and limiting or preferably sealing air leakage areas through the envelope; whereby interior air inboard of the envelope can flow freely outward into the then-most-strongly depressurized Separation Zone(s) created by a given wind, while outdoor air can not flow inward to replace it, so that the interior air pressure quickly falls toward equalization with the low pressure in such then-most-strongly depressurized Separation Zone(s), which interior depressurization greatly reduces net outward pressures on the envelope and so helps the envelope to remain intact even in hurricane force winds.

The most strongly depressurized Separation Zones are identified as those bordering the house perimeter walls and located “just around the corner” downwind of the outermost extremities of the house's then-windward walls(s) where windstreams have been pushed farthest off their original path and are being forced by the surrounding wind mass back toward their original direction. The method of identifying such ideally strong SZs and other aspects of the invention are better clarified in the following Detailed Description of the Preferred Embodiment, an application of most immediate utility and practicality: protecting the whole roof envelope of a house or similar building by letting the winds depressurize the attic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective sketch of a house “sitting on the bottom of a broad, deep river of wind”, the current flowing into, over and around it (large arrows). The winds push a positive (above atmospheric) pressure zone against the windward wall ((+) signs). The two up-turning arrows represent the broad vertically-diverted windstream which, on rounding over the windward fascia (roof edge) and being turned downstream again by the surrounding “river”, creates an over-roof Separation Zone or SZ ((−) signs), often the strongest over-roof depressurization. Since normal leakage areas and vents tend to maintain the attic air itself at or near ambient atmospheric pressure, this and other over-roof SZs (including immediately downwind of gables, not shown) can result in catastrophic net outward force on portions of the roof envelope.

The sideways-diverted winds, here represented by the arrows flowing around the right and left corners that are the extremities of the windward wall, create the off-wall SZs that the invention identifies ((−) signs) and utilizes to counteract such net outward forces, with air most strongly depressurized in these SZs. Each such ideally strong off-wall SZ will now be designated as “sSZ” in this text. Only one sSZ is visible here, 1; the other being out of sight around the far corner of the windward wall.

The invention's use of ideally-located valved openings is made clear: The valved soffit vent 2 facing down into the sSZ 1 remains open to the most strongly depressurized air below the vent 2, allowing attic air to flow out (small arrow) into area 1. At the same time, the windward valved vents such as 3 are pushed shut, blocking air entry—and the rain it can ruinously carry in; and other vents close also, wherever air tries to flow inward. The resulting depressurization of the attic ((−) sign, in the cutaway) strongly reduces any net outward pressures acting on the roof envelope.

(It can be seen that this valved vent method does nothing to hold the roof structure down on the walls below: the downward “suction” on the roof sheathing must equal the upward “suction” on the ceiling. This method is essentially a roof envelope saver, helping reduce forces so that the roof sheathing stays down, gables on and soffits and ceiling up—and blocking rain entry, which itself can bring the ceiling down.)

FIG. 2 is a perspective sketch from below of an early form of valved vent, mounted in a soffit vent, here hanging open as is normal. Recent designs are much lighter and more responsive, for good reason as noted below—and also for quieter operation in normal gusty conditions.

FIG. 3 a is a plan view of a typical rectilinear house indicating for given winds the extreme corners and therewith the strong sSZs flanking them. As noted above, the extreme corners are those which most widely separate the right and left diverted wind streams. In this simple case, which differs little from a plain rectangle, four extreme corners are seen, each being flanked by two most strongly depressurized sSZs, or eight in all. The wind from the North, N, creates sSZs marked N; the wind from the NE creates sSZs marked NE, and so on. Valved vents are installed facing into the sSZs, as indicated by a bar (-) just outboard of the wall, and generally in the soffit (roof perimeter not shown).

As can be seen, for a given wind direction to which the house will be exposed there will usually be two activated sSZs, one on one side and the other on the opposing side of the house. Concerning the other valved vents, any windward ones will blow closed immediately, while other “idlers” will face just weakly depressurized leeside outdoor air, and will let air into the attic until themselves “sucked” shut by the action of the fully depressurizing valved vents facing the then-strongest sSZs. Since these idler valved vents will outnumber the strongly fully-depressurized ones, and so offer more passageway, just a small inward pressure differential will allow them to feed as much air inward at first as the strongly-depressurized valved vents are emptying out, so tending to delay the full depressurization of the attic. So it's desirable to minimize the number of valved vents and to make them lightweight and responsive so they close quickly even in weak inward airflow.

FIG. 3 b is a plan view illustrating the locating of extreme corners and sSZs for a rather irregular house plan. Here, the influence of flow-interrupting protrusions and bays makes it more difficult to identify extreme corners for any and all wind directions; some redundancies and less usable or weakened corners must be considered. In the field, however, there's usually two and practically always at least one corner creating a fully depressurized and usable sSZ in any given wind. (Where there's only one, it may be best to double-up the valved vent area there.)

FIG. 4 a is a plan view of a notched corner, where the question-marked locations may be too short to accept valved vents and in any case will set up “muddied” sSZs, not ideally depressurized. The valves are therefore best placed as shown.

In FIG. 4 b, a tall, full bush such as a big rose bush illustrates an especially hurtful obstruction close to a corner. The sSZs (question marks) flanking what could have been an effective extreme corner can be largely spoiled, the wind's momentum dissipated as it pushes through the bush and fills in the depressions with air swirling back around it. Especially if sSZs are needed here (e.g. there's no corner on the other side of the building that can create sSZs for this wind), then the bush should at least be trimmed to half height.

FIGS. 1, 3 a and 3 b also show that having soffited overhangs around the entire building perimeter is ideal for easy and effective installation of sufficient valved vents. Common hip-roofed buildings almost always present this ideal configuration, but not-uncommon gable-roofed configurations usually do not. In the latter case it is feasible to use the attendant sSZ(s) by boxing in an opening for a valved vent (not shown), and/or using valved end-ridge vents or in some cases valved gable vents, these adaptations also venting normally until called upon in windstorms to depressurize the attic while blocking wind and rain entry.

The valved vents are each preferably sized so that the at-least-one active venting area is much larger than the total air leakage passages into the attic, ensuring that the depressurization effect can not be unduly weakened by air feeding inward through such leaks. (It may be desirable to carry out “gross leak sealing” of such leaks into the attic through the ceiling or directly from outdoors, and in any case that's usually desirable to reduce energy usage and moisture problems too. Again, the prior arts have included field studies of such leaks and of affordable methods of sealing.)

The attic depressurization efficacy of the strong sSZs and our valved soffit vents (and end-ridge and gable vents) has been proof-tested in lab and field, with models and an actual house, test conditions including gusty hurricane-speed winds with seemingly instant directional changes. With such swift changes shifting the job from one sSZ to another, the testing shows that valve action responds unfailingly: attic depressurization never falters. 

1. A method of reducing outward-acting forces induced by winds on a roof and other enveloping parts enclosing an attic or other roof space of a house or similar building, comprising steps of: identifying the location or locations immediately under the roof overhang around the house perimeter where the most strongly depressurized air will be created by a wind stream flowing around the house, being the location or locations immediately downwind of the outermost extremities of the house's then-windward sidewall(s) where the building-diverted windstream has been pushed farthest off its original path and is being forced back toward its original direction; or, where there is no suitable roof overhang, similarly identifying the most strongly depressurized off-roof location or locations such as downwind of the top of a gable end; and repeating the step for all wind directions to which the house is exposed to identify all such potentially most depressurized locations. 